Greens mowers are well known machines used for cutting grass to extremely low heights of cut. As such, they are used primarily for cutting grass on golf greens and the like. Typical greens mowers have a plurality of reel type cutting units carried on a frame with the frame being supported by ground engaging wheels. Greens mowers come in both walk behind and riding versions. The Toro Company of Minneapolis, Minn., is a well known manufacturer of such greens mowers.
Many riding greens mowers built by The Toro Company have a three wheel or tricycle configuration. In other words, the frame of the vehicle is supported by three ground engaging wheels comprising two front drive wheels and a single, steerable rear wheel spaced between and set rearwardly from the two front drive wheels. The frame carries an engine in the rear located generally over the rear wheel, a seat for the operator, and a steering wheel for allowing the operator to turn the rear wheel to guide the greens mower.
In addition, the greens mower frame typically carries three reel type cutting units also arranged in a tricycle configuration. Two front cutting units are placed in advance of the front drive wheels with a third, center cutting unit being arranged rearwardly of and in the center of the frame behind the two front cutting units. The Greensmaster 3100 built and sold by The Toro Company is a typical greens mower of this type.
The Toro Company also builds other riding mowers which are quite similar to greens mowers, but are adapted to mowing other portions of a golf course, e.g. fairways, tees and the like. One such vehicle is the Reelmaster 216 which is also built and sold by Toro. Like the Greensmaster 3100, the Reelmaster 216 is a three wheel vehicle with three reel type cutting units arranged at the front of the machine.
Some differences do exist between fairway mowing units and greens mowers. For example, the Reelmaster 216 has a front mounted as opposed to a rear mounted engine. Another difference relates to the type of tires used on the wheels. A greens mower cannot risk marring or scuffing the surface of the greens and, thus, uses bald tires without any tread. However, such tires have relatively poor traction. A fairway mower, such as the Reelmaster 216, would use treaded tires.
Riding mowers of the type just described are often powered by hydraulic drive systems. Such systems include individual hydraulic drive motors applied to selected ones of the drive wheels and driven by a conventional hydraulic variable speed pump. In many greens mowers, including the Greensmaster 3100, just the front drive wheels are driven to provide a two wheel drive. However, in other cases such as in the Reelmaster 216, at least one version of this product is sold in which all three of the drive wheels can be driven to provide three wheel drive. Three or all wheel drive generally provides superior traction.
One difficulty faced by these types of products, and particularly with greens mowers, is a tendency for these products to have at least one of the drive wheels slip, and thus lose traction, under various operational conditions. This will bring the vehicle to a halt, requiring the operator to back the vehicle up or perform some other maneuver to regain traction and regain the ability to drive. This is a major annoyance while mowing especially if it happens frequently. It cuts down on the productivity of the mower requiring that a longer time be spent mowing a particular area of grass.
The tendency for drive wheel slippage in such vehicles is brought about, in part, by their unusual geometry and weight distribution as well as by the environmental conditions they encounter while operating. These mowers, particularly mowers like the Reelmaster 216, are often used to mow quite hilly areas, e.g. the hills and swales in the fairways or around greens, bunkers, tees and the like. Often, they traverse the hill in a sideways or diagonal fashion with the uphill drive wheel carrying little of the vehicle's weight. The grass is often wet and thus relatively slick. In addition, when making a cutting swath across the hill, the cutting units will be placed down on the ground so that their weight is not being carried by the vehicle frame but by the ground.
Given the relatively small overall weight of the unit to begin with, the uphill wheel in this scenario will often slip and lose traction, bringing the unit to a halt. The operator then has to somehow maneuver the unit, by backing it up or allowing it to roll back down the hill, to regain traction. The disadvantages of this are apparent as discussed above.
As noted earlier, the Reelmaster 216 is sold in a three wheel drive version which offers better traction than the two wheel drive version. However, the hydraulic drive system for this vehicle connects all of the wheel drive motors in parallel to the source of the pressurized fluid, i.e. to the hydraulic pump. This is done in part to provide a natural differential action to allow the various wheels to turn at different speeds during a turn. However, in such a drive system, when any one wheel starts to slip, the system naturally tends to supply more fluid to the slipping wheel motor, thus reducing the tractive effort from the other drive wheels. Thus, even in the known three wheel drive versions of the Reelmaster 216, when one of the front drive wheels starts to slip, generally the uphill wheel during a diagonal traverse across a hill, the unit will still come to a stop.
One might think that a hydraulically driven greens mower, which ostensibly mows just the surface of a golf green, would be less likely to encounter wheel slippage conditions than a product like the Reelmaster 216 which is meant to mow more hilly areas of the golf course. However, the reverse is generally true with wheel slippage often being a more acute problem in a greens mower. This is due primarily to the less favorable weight distribution in a greens mower, arising from the use of a rear mounted engine that is not located over the front drive wheels, to the use of a two wheel drive system, and to the use of bald tires which have no traction enhancing tread. It is also due to the fact that such greens mowers are not immune from having to traverse hilly areas.
For example, it is common when cutting a golf green with a riding greens mower to make a first cutting swath across the green, to turn around in a tight circle off the surface of the green, and to then come back and make a second cutting swath across the green which is immediately adjacent to the first swath but in an opposite direction. During the time when the operator is turning the greens mower around, i.e. after having finished the first cutting swath and preparatory to making the second swath, he or she is often turning in a tight circle immediately adjacent the green. Many golf greens have hills or valleys in this area such that the greens mower often has to drive up or across a hill when turning around. This is when a greens mower is most likely to, and often does, lose traction on the uphill wheel and come to a stop.
In addition, many golf greens today are quite sculptured and may have different elevational levels or steps. Typical greens mowers may not be able to climb such steps. This may require that the stepped portion of the green be mowed with a walk behind greens mower, which is obviously less efficient than being able to simply mow the whole green with a riding greens mower. Other golf greens may be so steeply inclined that a conventional greens mower may not be able to drive up the incline of the green. Such greens can only be mowed in one direction, namely downhill, requiring that the operator drive around the outside of the green after each cutting swath to reposition the greens mower above the green before the next cutting swath. This is obviously a time consuming, and thus undesirable, process.